A step of processing a semiconductor wafer comprises a step of adhering a surface protecting adhesive film for a semiconductor wafer to a circuit-formed surface of the semiconductor wafer, a step of processing a non-circuit-formed surface of the semiconductor wafer, a step of peeling a surface protecting adhesive film for the semiconductor wafer, a step of dicing for dividing and cutting the semiconductor wafer, then a step of molding for sealing the semiconductor chip with a resin for protecting the outer portion, and the like.
Conventionally, in a step of processing a non-circuit-formed surface of a semiconductor wafer, when thickness of the semiconductor wafer is removed to be as low as 200 μm, strength of the semiconductor wafer itself might be deteriorated due to a damaged layer caused by a mechanical grinding and the semiconductor wafer might be broken due to a minute stress. On this occasion, if a thickness of the semiconductor wafer is less than 200 μm, a non-circuit-formed surface of the semiconductor wafer is mechanically grinded and then a step of chemical treatment is additionally carried out in order to remove a damaged layer generated on the non-circuit-formed surface of the semiconductor wafer.
As an etching step of a chemical treatment, a wet etching step has been carried out, which uses mainly a mixture of fluorine and acetic acid. A circuit-formed surface is faced downward while a non-circuit-formed surface is faced upward to fix surrounding portions of a semiconductor wafer with clamps in a state that the semiconductor wafer is exposed with a nitrogen gas. The thus-clamped wafer is rotated at a high rate and an etching solution dropwise from the top at the same time. In this way, a wet etching step for processing a non-circuit-formed surface of the semiconductor wafer has been carried out. However, from the viewpoint of an environment, the treatment of a waste solution and the like has been worried.
In late years, a step of removing a damaged layer generated on a non-circuit-formed surface of a semiconductor wafer has been examined as an etching method in consideration of an environmental aspect by a plasma etching using plasma. However, inside the system is made at high temperatures and in vacua in order to generate plasma, thus resulting in breaking a semiconductor wafer or causing a fusion of an adhesive film in some cases. Further, there is a problem in that it is not possible to transport a semiconductor wafer from a chuck table.
Further, as an alternative step, a step of sputtering or evaporating a metal on a non-circuit-formed surface of a semiconductor wafer that was thinned after grinding a non-circuit-formed surface of a semiconductor wafer has been examined. Since the temperature and vacuum conditions are added in the same manner as the above plasma etching step, tapes might be greatly damaged.
In late years, the thinning of a semiconductor chip has been in high demand, and a chip having a thickness of from 20 μm to 100 μm has been required. In the mean time, a manufacturing process of a semiconductor wafer has been complicated. A protecting method for a semiconductor wafer capable of preventing the thus-thinned semiconductor wafer from the breaking and the processing various back side in a state that a semiconductor wafer is adhered to a substrate supporting the semiconductor wafer via a surface protecting adhesive film for a semiconductor wafer has been demanded as a step of processing a non-circuit-formed surface of a semiconductor wafer.
An example of a protecting method is disclosed in JP2001-77304A. In this patent is disclosed a method of joining a holding substrate having a thickness of more than 0.2 mm to a circuit-formed surface of a semiconductor wafer via a thermoplastic resin layer, and processing a non-circuit-formed surface of a semiconductor wafer. However, a method of this type might cause some problems such as a contamination of a semiconductor wafer and the breakage of a semiconductor wafer during the grind as stress of grinding pressure could not be absorbed in case of a further thinned wafer.